This invention relates to methods and apparatus for locating and marking the center of turning squares, billets and other objects to be placed in a lathe.
It is desirable in preparing turning squares, wood billets and other objects to be mounted in a lathe for machining to locate on the object the positions on its opposite ends which define between them the line or axis which will be most nearly "centered" within the object. Mounting the turning square or billet so that it rotates about this axis will make it possible to obtain a cylinder or cylindrical section which is as large in diameter as possible for a given turning square or billet and will minimize vibration when the billet is subsequently rotated in the lathe.
For a turning square or billet which has a truely square cross section, the desired center point on each end of the billet lies at the intersection of the two lines which intersect the diagonally opposite corners of the square end surface. This point has traditionally been located and marked in the prior art by positioning a straight edge across the billet end and drawing with pencil or scribing lines between the corners. Frequently, shallow saw kerfs are made on those lines to facilitate engagement of spurs in a lathe drive center. Alternatively, the center point is sometimes located simply by sawing a shallow kerf between each pair of opposite end corners. These techniques are time-consuming and require sometimes awkward manipulation of the turning square or billet and marking instruments. Furthermore, separate layout and marking of each square or billet is required. Consequently, a variety of center marking devices have previously been developed, some of which are intended primarily for use in metal turning and others of which are intended for wood turning. Examples of such devices are represented in U.S. Pat. No. 49,533 to Safford and Sawyer, 311,619 to Varnum, 316,918 to Standeford, 364,082 to Bell, 906,180 to Wrightsman, 912,052 to Albertson and 4,667,549 to Griffon. However, none of these marking devices and techniques provides a simple to manufacture and simple to use device which can rapidly and accurately mark turning squares or billets having a variety of shapes and dimensions without the need for any measurement of the billet or adjustment of the device.